Heat exchange is important to ensure devices remain within acceptable operational parameters as well as to achieve efficient thermodynamic operation. A great deal of effort has been directed toward improving thermodynamic efficiency in chip package heat exchangers. As such, numerous heat exchange systems have been developed for removing heat in a uniform, single chip package.
However, modular packages, which include a number of integrated circuit chips, have become more prevalent in the electronics industry. The chips within a module may be structurally equivalent, such as an array of similar memory chips. Alternatively, the chips may be structurally different, such as a set of chips consisting of a read only memory chip, a random access memory chip, a microprocessor and an interface chip.
One issue with multi-chip modules is the increased density of the chips on the package. This confinement within a single area increases the need for high performance cooling. Previously, the use of a liquid coolant that is forced to flow through a multi-chip module to absorb thermal energy, where the liquid coolant is removed from the module at an outlet port, has been shown. While, a liquid coolant loop through a module is an effective way of ensuring adequate cooling, it is an expensive cooling method that requires a mechanism for providing a forced flow of liquid coolant.
For applications in which forced liquid cooling is impractical, heat spreaders, or sinks, are used to dissipate thermal energy. For packages that generate a significant amount of thermal energy, the thermal path from the chips to the exterior of the heat spreader is of particular importance. It is often desired that contact be made between the integrated circuit chips and the structure that begins the thermal path to the sink. However, large-chip and multi-chip assemblies have a non-uniform height across their area. During the fabrication of these assemblies, there will be differences among the modules and even among the various chips within a single module. For example, chips are often encased within a carrier before being mounted to a substrate. The carriers may have slight differences in height and/or the mounting of the chips to the substrate may result in slight variations in height or angle with respect to the component surface of the substrate. Various fabrication and machine tolerances are additive, so that the chips within a multi-chip module will not have a planar surfaces across all chips.
Ensuring adequate contact between individual chips and a heat dissipating structure is difficult in many applications. Available air-cooled heat sinks are too stiff to adapt to such non-uniform or warped shapes of chips or to shape-changing chip surfaces during operation. Lidded packages allow to flatten warped assemblies and to adapt lids to multi-chip topologies, both within the manufacturing environment (clean, controlled). The thermal spreading of the lid renders the package tolerant to non-uniformity of heat sink attachments. Lids create an additional thermal resistance and therefore perform poorer than direct-attached heat sinks. Also, there are no compliantly attached lids available. Thus, the thermal envelope of operating the chips using the current state-of-the-art is limited.
What is needed is an apparatus that can provide a heat transfer interface in packages containing non-uniform chip assemblies.